Invasion by the exotic grass Microstegium vimineum (Japanese stiltgrass) negatively impacts native tree regeneration and herbaceous species

Invasions of exotic plants have often been correlated with alterations in the diversity and productivity of native ecosystems. However, few experimental studies have been conducted to quantify the community impacts of invasions. The purpose of this study was to experimentally determine the effects of invasion by the exotic annual grass Microstegium vimineum (Japanese stiltgrass) on native trees and herbaceous species. Microstegium is a highly shade tolerant C₄ annual grass that is rapidly increasing in eastern deciduous forests. When it invades it creates dense monotypic stands that may impact forest communities by inhibiting tree regeneration and herbaceous species productivity. To experimentally test for community-level effects of Microstegium invasion, we created replicated early-successional forest communities containing nine species of tree seeds or saplings plus twelve herbaceous species. Half of all plots were randomly assigned to be seeded with Microstegium. After one year, invasion by Microstegium reduced herbaceous species productivity by 82% and species richness by 24%. Tree seedling survival for small-seeded trees was reduced by 27% overall, but the size of the effect differed among tree species. Ongoing data collection will quantify the impact of invasion on tree sapling survival and growth. These preliminary results indicate that invasion by Microstegium can inhibit forest regeneration, reduce herbaceous layer richness and productivity, and alter forest community composition.